1. Field of the Invention
The present invention relates to a hard coating film, a method of forming a hard coating film, and a material coated with a hard coating film. More particularly, the invention relates to a hard coating film formed on a substrate for enhancing the wear resistance thereof in the fabrication of cutting tools to be used for such purposes as metal cutting, drilling and end milling, metal dies to be used for such purposes as forging, press molding and extrusion molding, and jigs and tools to be used for such purposes as punching in plastic metal working.
2. Description of the Related Art
Conventionally, on a cutting tool made of a substrate such as cemented carbide, cermet or high-speed tool steel, for example, a hard coating film formed of such a substance as TiN (nitride of Ti), TiCN (carbonitride of Ti), or TiAlN (complex nitride of Ti and Al) has been provided for enhancing the wear resistance thereof. In particular, as disclosed in Patent Document 1 indicated below, a hard coating film formed of TiAlN, which has excellent wear resistance, is becoming prevalent in lieu of a hard coating film formed of TiN or TiCN. However, there is still an increasing demand for a hard coating film having higher resistance to wear in order to meet an increase in hardness of work materials and an increase in cutting speed required therefor in recent years.
An example of a hard coating film formed of oxide is found in Patent Document 2 indicated below, which discloses the following description: When a layer consisting essentially of an oxide of aluminum is formed at low temperature, a high degree of hardness cannot be achieved due to occurrence of an amorphous state. Therefore, for forming a crystalline oxide coating film at low temperature, it is proposed to use a complex oxide material (Al, Cr), which contains chromium that is an element capable of forming an oxide substance having the same crystalline structure (corundum) as that of an oxide of aluminum and capable of providing crystalline oxide formation at low temperature. However, in the use of this complex oxide material (Al, Cr), the crystallinity of an oxide coating film formed is unsatisfactory due to residual amorphousness, giving rise to difficulty in achieving a high degree of hardness.    Patent Document 1:
Japanese Patent No. 2644710    Patent Document 2:
Japanese Patent No. 3323534